Optical evaluation of deposition thickness and measurement of permeate flux enhancement of simulated fruit juice in presence of turbulence promoters

Ultrafiltration of simulated fruit juice (pectin and sucrose) is performed in continuous cross-flow mode with an organic ultrafiltration membrane (poly phenylene ethersulfone, PPE 30) of 30 K molecular weight cut off. The permeate fluxes are measured under different operating conditions of pressure, cross-flow velocity and pectin concentration. Significant enhancement of permeate flux is achieved by incorporation of straight cylindrical promoters placed across the flow. The optimum number of such promoters and their sizes are evaluated. Image analyzing video microscopy is successfully used to accurately quantify the deposition of pectin molecules on the membrane surface. The deposition thickness decreases with increase in cross-flow velocity, increases with pectin concentration but is less susceptible to increases in pressure. The effects of the shape of the promoters on flux enhancement and deposition thickness are also investigated in detail and approximately parabolic shaped promoters are chosen with further increases in flux enhancement (keeping the number of promoters same as in the case of straight promoters). The deposition thickness profiles around a promoter and the average deposition thickness on the whole membrane are optically measured and the consistency of the results in relation to enhancement of permeate flux are examined.